New World Screwworm Detected Near Chicago, Heightening U.S. Livestock Concerns

The U.S. Department of Agriculture (USDA) reported on Friday that workers detected the New World screwworm (NWS) in a six‑month‑old sheep near the U.S.-Mexico border in Coahuila, Mexico. The case is the closest the parasite has come to the United States since the 1960s eradication program. The screwworm’s larvae feed on living tissue; if untreated they can cause severe pain, infection, and death in livestock. Experts warn that if the fly spreads into U.S. territory it could threaten the cattle industry—making Texas, the country’s largest beef producer, vulnerable to outbreaks that could cost billions. The livestock herd is already at a low level after the pandemic, and rising beef prices risk further inflation. In response, the USDA and Mexican authorities have been coordinating containment measures, including the release of millions of sterile male flies. This sterile‑insect technique has been successfully used in past eradication campaigns and is the most effective tool for disrupting the pest’s reproduction cycle. Additionally, the U.S. has blocked cattle imports from Mexico for over a year to limit the parasite’s spread. The detection has prompted a virtual briefing by Agriculture Secretary Brooke Rollins, who emphasized that federal officials are monitoring developments closely and that movement of animals remains the primary vector for the fly’s northward migration. National and state agencies have also established quarantine zones and increased surveillance of livestock around southern Texas. While the threat to humans is low and does not compromise food safety, the potential for widespread livestock losses underscores the importance of continued vigilance and rapid response. The outbreak remains confined to Mexico and the border region, but officials say that the proximity of recent detections elevates concerns for producers and the broader agricultural economy.